An irrigation system is limited not by the size of the yard but by how much water your supply can push at once. Total the flow your sprinklers want, compare it with what the tap actually delivers, and the number of zones falls out. Everything downstream depends on getting the supply flow right.
How many sprinklers at once
Divide your supply’s flow by one sprinkler’s flow. A spigot delivering 8 GPM (30 L/min) runs about three or four 2 GPM (8 L/min) spray heads at a time — try to run more and every head sputters. That per-zone limit, not the yard size, is what dictates the zone count.
Measure your supply first
The bucket test: time how long your supply takes to fill a 5-gallon bucket flat out, then GPM = 300 ÷ seconds. A 5-gallon bucket in 30 seconds is 10 GPM. Do it at the time of day you will irrigate — municipal pressure, and therefore flow, drops in the morning peak when everyone waters.
Irrigation Flow Calculator
Total your sprinkler flow in GPM, compare it with your supply, and see how many zones you need.
How many zones
Zones = total sprinkler demand ÷ usable supply, rounded up. Sixteen heads at 2 GPM (7.5 L/min) is 32 GPM (120 L/min) of demand; on an 8 GPM (30 L/min) supply that is four zones, each running in turn off its own valve. Leave a margin so zones don’t run at the ragged edge.
What flow do sprinklers use?
| Head type | Typical flow |
|---|---|
| Fixed spray heads | 1.5–2.5 GPM (6–10 L/min) |
| Rotors | 2.5–5 GPM (10–20 L/min) |
| Drip emitters | 0.5–1 GPH (2–4 L/h) each |
Drip is a different world — hundreds of emitters fit on one zone. Flow rises and falls with pressure, so check the nozzle chart for your heads at your pressure.
Why sprinklers reach less than advertised
Pressure. Nozzle charts quote throw at a stated pressure (often 30–45 psi / 2–3 bar); friction in undersized pipe and too many heads per zone eat it, shrinking the radius and coarsening the spray. If coverage is weak, split the zone or upsize the supply pipe rather than adding heads.